Vol 61 Iss. 2

Assessment of the degree of similarity or difference of geological structures has always been of interest to researchers, as it has practical consequences: questions of genesis of structures and forecasts of distribution of mineral deposits are largely solved taking into account possible analogies. The complexity of this assessment is aggravated by the fact that the objects of nature, unlike the products of human technological activity, in some features are necessarily inimitable. Even in the simplest cases, one can expect in advance some difference in nearby structures having the same origin. A significant difficulty is the selection of those indicators (attributes) by which the degree of closeness of the compared geological structures is assessed. Emphasized interest in certain aspects (genesis, ore-bearing, metamorphism, etc.) may manifest itself in the fact that some features in comparison with others will subjectively receive greater importance, while some will be completely left out of the analysis.

Based on the vast experience of seismic exploration in oil and gas bearing areas, the methodology and systems of observations by reflected and refracted waves in relation to the study of hollow structures of sedimentary rocks have been well developed and are still being improved. At the same time, in recent years, seismic exploration method is increasingly used to study the consolidated crust and, in particular, structures composed of highly metamorphosed and crystalline rocks in regions where ore deposits are being searched for. Under these conditions, seismic exploration is tasked with studying very complex folded and highly dislocated structures formed by rocks that are relatively poorly differentiated in terms of elastic wave propagation velocity.

The search for ore bodies of increased electrical conductivity by the method of dipole inductive profiling with amplitude-phase measurements is based on the study of changes in the magnetic field of a harmonic magnetic dipole depending on its movement along the profile (relative to the ore body).

Precambrian platforms and shields, occupying the main part of the territory of the continents and storing in their bowels huge reserves of minerals, are not sufficiently studied geologically. Dissection and correlation of Precambrian strata by classical methods of paleontological, petrographic and structural-geological analysis are extremely difficult, as deeply metamorphosed and granitized rocks in many cases retain only relict textural and lithological features of the original geological formations. Geophysical methods, in particular, gravity and magnetic exploration, have great potential in studying the structure and reconstructing the history of development of Precambrian shields.

The existing methods of determining the parameters of geological objects by gravity anomalies are associated with the approximation of the original data by analytical expressions, the parameters of which are subject to determination.

As is known, electrical exploration methods identify well-conducting objects, which can be both sulfide bodies, and graphitized zones or zones of tectonic disturbances. While the latter can often be identified using amplitude and phase components of the eletromagnetic field during dipole profiling, it is still impossible to separate anomalies associated with sulfide ores and graphitized zones using electrical exploration.

Under dipole inductive profiling (DIP) is understood a sequential study of the amplitude and phase of the magnetic field of a harmonic magnetic dipole, performed with simultaneous movement of the dipole generator and dipole-measuring device (measuring point) along a certain direction (profile) on the surface of the earth. The reciprocal spatial position of the dipoles (generator and receiver frames) is kept constant during profiling, so the relative field changes at the measurement points are only a function of the geoelectric cross sections of the areas traversed by the installation...

The advantage of dipole inductive profiling (DIP) is the optimal coupling of exciter, sensor and the object of interest, which is technically easy to realize. At the same time, practically comparable in many cases with other inductive methods depth is achieved by using simplified portable equipment, which allows to significantly increase the productivity of electrical exploration.

The industrial oil shale reservoir of the Leningradskoye field is confined to the Kuker horizon of Ordovician limestones. The thickness of the overlying strata varies from 50-60 m in the north to 80-100 m in the south. In the northern part, Ordovician limestones are directly spread under Quaternary sediments; in the southern part, apart from Quaternary sediments, they are overlain by Middle Devonian sediments (marls, sands and clays). The thickness of Quaternary sediments averages 5-10 m.

The method of borehole magnetic exploration is currently applied almost exclusively to magnetite deposits of various genetic types. There is practically no experience in staging this method on relatively weakly magnetic objects. This is explained mainly by insufficient resolution of modern borehole magnetometers, which do not allow to measure the magnetic field in the borehole with an accuracy higher than ± (1000 - 1500) gamma for the full field vector and 500 gamma for its vertical component.

One of the important tasks of borehole logging in ore districts is to delineate ore intervals and determine the metal content of the ore. At the sulfide copper-nickel deposits of the Pechenga region, the complex of geophysical methods now confidently distinguish only the zones of sulfide mineralization, to which the ores are confined...

Significant volumes of drilling for prospecting and exploration of copper-nickel ores within the Pechenga and Alla-Akka-Yarva ore fields determine constant efforts aimed at improving well logging and increasing its efficiency. By the present time the issues of complexing of standard logging methods have been solved and the possibilities of both the complex as a whole and individual methods have been clarified in identifying the main types of rocks and ores.

Vertical seismic profiling (VSP) in wells of the Pechenga region is carried out in conditions of steep dip of geological boundaries, and the wells themselves are inclined (zenith angles of 5 - 20°).

In 1968, a seismic station with intermediate magnetic recording POISK-1-48-KMPV-OV was introduced into the practice of regional seismic works on the Baltic Shield. The use of magnetic recording made it possible to analyze seismic materials in laboratory conditions in order to decipher the interference sections of the wave field for a more reasonable correlation of the main waves in the interference zones.

Seismic materials obtained during detailed studies in the Pechenga district of the Murmansk region are characterized by the presence of a large number of unextended in-phase axes, on which subsequently reflecting elements are constructed by the apparent velocity method...

At joint application of several geophysical methods of researches the approach is widely used, at which on the basis of the data of separate methods special corrections are calculated, introduced in readings of other methods. This significantly increases the detail and certainty of the general conclusion about the identified features of the geological structure...

The specificity of the problem under consideration is that the analytical expressions of the Z_a and ∆T fields include not the dip angles themselves, but some auxiliary angles (respectively, v and e), which depend not only on the direction and dip angle, but also on the inclination of the magnetization vector and the azimuth of the formation strike.

In permeable rock formations, natural filtration of formation water can be observed, corresponding to its movement from the supply area to the discharge area. If a well intersects such rocks, this phenomenon affects the temperature regime of the medium in it.

Stationary groundwater filtration affects the thermal state of rocks and creates anomalous temperature distribution in wells. The amplitude of the temperature anomaly in such geothermograms recorded in wells under steady-state thermal regime can be used to calculate the filtration rate in the aquifer using the formulas...